Prisoner bags a prison without any cracks? (4-4)
I believe the answer is:
cast-iron
'without any cracks?' is the definition.
I can't judge whether this definition defines the answer.
'prisoner bags a prison' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'bags' is an insertion indicator (bag can mean secures or steals).
'prison' becomes 'stir' (informal term for prison).
'a'+'stir'='astir'
'con' placed around 'astir' is 'CAST-IRON'.
Can you help me to learn more?
(Other definitions for cast-iron that I've seen before include "Rigid, unyielding" , "Very strong" , "Firm and unchangeable" , "Extremely robust" , "Unassailable" .)